1. Field of the Invention
The present invention relates to a titanium compound for photochemical reactions and a method for producing the titanium compound.
2. Description of the Related Art
It has been known that titanium oxide generates electrons and holes which exert strong oxidation and reduction actions on the surrounding substance upon photoexcitation. These reactions are utilized for oxidation and reduction of water, decomposition of hazardous substances, sterilization, and inorganic and organic syntheses.
Titanium oxide having a large specific surface area and good crystalline properties performs efficient photochemical reactions. Production methods for such titanium oxide are reported as follows:
(1) J. Mater. Sci. Lett. 15, 197 (1996); a process comprising dissolving titanium alkoxide in toluene and hydrolyzing it in an autoclave by supplying water from the gas phase, while growing crystals simultaneously. PA1 (2) Mater. Chem. Phys., 17 (1987) 87-101; a process comprising of intercalating titania between montmorillonite layers. PA1 (3) Japan Chemical Society, 71st Autumn Annual Meeting (1996), Preprints, p. 94, 4P1, .beta.24; a process comprising of intercalating titania between montmorillonite layers (as in (2) given above) and subsequent hydrothermal treatment. PA1 (4) 15th "Symposium on photocatalyst chemistry", p. 29; a process for producing TiO.sub.2 powder having a tunnel structure from K.sub.2 Ti.sub.4 O.sub.9. PA1 (5) Electrochemical Society, 1996 Autumn Meeting, Synopses, p. 234, 1112; a process for producing fine particles by utilizing the aqueous phase in reversed micelle. PA1 (6) Japanese Laid-Open Patent Publication No. 8-182934; a process comprising doping or coating titanium oxide with a potassium compound and/or a phosphorus compound and an aluminum compound for improving efficiency.
The problems with the conventional fine highly crystalline titanium oxide powder are that the titanium oxide powder tends to aggregate and that the reaction product has difficulty in accepting diffusion of materials as the primary particles of the titanium oxide powder decrease in size. These properties cause a low catalytic activity per unit surface area. There is also thermal deterioration of the titanium oxide powder.
These problems can be solved if ultra-fine particles of titanium oxide are supported on a carrier without aggregation. Doing so, however, has the disadvantage of limiting the catalytic activity per unit volume or weight because of the carrier mass.
It has been proposed that the problem might be solved by using titanium oxide particles of irregular shape, such as a needle rather than a sphere. However, such titanium oxide shows good selectivity but poor catalytic activity.
Accordingly, there is a demand for a titanium compound used for photochemical reactions having very high catalytic activity per unit surface area and extremely high stability to heat. There also is a demand for a method for producing such a titanium compound.